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An advanced brain scanning technique has shown for the first time in humans how concussion damages the brain and its wiring, findings that cast doubt on the effectiveness of conventional assessment tools used by doctors.

This new understanding of the physical damage to the brain and the time frame for recovery suggests athletes should not be cleared to play less than two weeks after a concussion and should probably be shelved much longer, said Alex Rauscher, an MRI scientist and Canada Research Chair in the department of pediatrics at the University of British Columbia.

“We can see that the myelin is still (damaged) at two weeks, so even if the athlete passes the neuropsychological exam, I would hold him out of play for at least three weeks,” he said. “Getting another concussion before the brain is healed can be extremely dangerous.”

High-level athletes are notorious for trying to return to action quickly after a mild traumatic brain injury. Only 31 per cent of NHL players took more than 10 days off after suffering a concussion, according to a separate study published in the Canadian Medical Association Journal. Recovery time more than doubled with each successive concussion.

Raucher used specially tuned magnetic resonance imaging (MRI) of hockey players — who are at a high risk of concussion — to detect damage to the myelin sheath that protects nerves in the brain.

Myelin, which acts like the insulation on a wire, is the substance that is damaged in patients with multiple sclerosis.

The researchers scanned the brains of male and female university hockey players before the start of the season and then did multiple followup scans on eleven players who suffered a concussion, three days, two weeks and two months after the injury.

“We didn’t really know what happened to the brain in a concussion, because until now we haven’t had data taken before the injury to compare,” said Rauscher.

Concussions damage myelin and appear to cause the insulator to separate from the nerve and then slowly recover over two months, he said.

The researchers also noticed that conventional concussion assessments conducted in parallel with the scanning program failed to reflect the persistence of myelin damage.

Doctors rely on observations of behaviour, patient reporting of symptoms and questionnaires to determine whether a player has recovered before returning to play after a concussion.

“There was no correlation between the questionnaire results and the imaging findings,” he said. “It couldn’t see the damage to the brain.”

That puts doctors in a position in which they could send players back to the ice who are not fully healed, he said.

Conventional MRIs also detected a reduction in brain volume — equivalent to three sugar cubes — both in players that suffered concussions and in players who had not suffered a concussion scanned after the grind of a normal hockey season.

The volume reduction, probably the result of a number of sub-concussive hits, is also found in extreme-long-distance runners, said Rauscher. The runners’ brains recover over time, but it is not known if hockey players fully recover brain volume in the break between seasons.

At UBC student athletes return to play in a graduated program that begins when the athlete is “essentially symptom free,” after which they return to classes, a gradual return to exercise, then return to sport, said Dr. Rob Lloyd-Smith, head physician to the UBC Thunderbirds sports teams. Doctors also conduct a computer-based neuropsychological test to compare with pre-season baseline testing.

“We rely on a number of clinical assessments and tools for diagnosis, but there is a significant overlap in symptoms between different conditions like concussion and whiplash, or even a viral illness that can make you feel lousy,” he said.

Doctors are waiting for a test that is both accurate and specific to concussion, a test that won’t be confused by other conditions, he said.

“Although there were changes in the myelin, it is uncertain what this represents and we are not ready to use the changes to determine return to play,” Lloyd-smith said.

While MRI provides a window into the kind of damage that concussion inflicts on the brain, it is not yet realized as a diagnostic tool.

“We don’t have ideal tools at present, but we do have access to a student athlete population that is ideal for this kind of research,” he said. “The tools that we have right now are not the tools that we will have 10 years from now, but they are better than the tools we used 10 years ago.”

Rauscher’s findings were published in the peer-reviewed open access journals PLOS One and Frontiers in Neurology.

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